That question and answer are a bit unclear, but I think they show a fundamental misunderstanding. If you overwrite a file using cp, the overwritten file disappears. It doesn't matter if that file used to be sparse; these things are not contagious.
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TobuJul 20 '13 at 13:40

Interesting, but I assume that the source file still exists. The question is if I can preserve this feature.
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d33tahJul 20 '13 at 14:01

1 Answer
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The solution is apparently to use cp --sparse=always. My first attempt was with writing some Python code, but unfortunately the MD5 sums didn't match (could anyone tell me why? the code's in edit history).

The filesystem block size usually isn't 512B - more often it is 4KB.
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peterphJan 9 '13 at 22:05

You say that might be the reason that MD5 sums didn't match?
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d33tahJan 9 '13 at 22:10

No, filesystem gives you zeros where it finds an unallocated block, so the error had to be in your script. The block size is important for other reason: if you seek by 6 empty 512B sectors, then one with some data an then again seek say 4 empty sectors, you save nothing, because the data in the one sector causes the fs to allocate whole 4K block.
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peterphJan 9 '13 at 22:35

@d33tah your python code is losing a byte every time it seeks because of the -1 in the seek target, which isn't necessary. You should seek ahead a full 512 bytes each time.
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Wumpus Q. WumbleyJul 20 '13 at 17:37